Steam generating, superheating, and resuperheating plant



March 24, 1959 A. LIEBERHERR STEAM GENERATING, SUPERHEATING, ANDRESUPERHEATING' PLANT Filed Jan. 31, 1955 2 Sheets-Sheet l INVEN TOR.

A ETH we L IEBEEHEE/E.

A TTORNEJ arch 24, 1959 LIEBERHERR 2,878,791

STEAM GENERATING, SUPERHEATING, AND RESUPERHEATING PLANT Filed Jan. 51,1955 2 Sheets-Sheet 2 INVENTOR. ,4 RTHUI? L [Ease/HERE.

United States Patent STEAM GENERATING, SUPERHEATING, AND RESUPERHEATINGPLANT Arthur Lieberherr, Winterthur, Switzerland, assignor to SulzerFreres, Societe Anonyme, Winterthur, Switzerland, a corporation ofSwitzerland Application January 31, 1955, Serial No. 485,061Claimspriority, application Switzerland February 10, 1954 3 Claims. (Cl.122-478) The present invention relates to a steam generating,superheating, and resuperheating plant.

The resuperheater of the plant according to the invention includes aheat transfer apparatus which is placed inside the steam generator andin which heat is indirectly exchanged between a high pressure operatingfluid, which is heated in tubes forming part of the generator, and thesteam to be resuperheated.

'The heat transfer apparatus is formed by a group of outer tubes orconduits and a group of tubes disposed inside the outer tubes. If thesteam to be resuperheated, which is partly expanded, is conductedthrough the outer tubes and the high pressure fluid is conducted through"the inner tubes, the heat transfer apparatus is preferably disposed ina part of the steam generator where the apparatus is protected againstradiant heat. In this case, "the partly expanded steam exchanges heatwith the combustion gases and with the high pressure fluid. If thecombustion gases and/or the high pressure fluid are hotter than thesteam to be resuperheated, the resuperheating process requires lessheating surface and is performed more quickly than in a resuperheatingprocess in which a part of the heat is indirectly transferred outside ofthe steam generator from high pressure steam to the steam to beresuperheated, and in which another part of the heat is transferredinside the steam generator from hot combustion gases to the steam to beresuperheated. Radiation losses of an indirectly heated resuperheaterportion'placed outside of the steam generator are avoided with "the"arrangement according to the invention. Aside from this, no additionalspace is required outside of the steam generator and pressure lossescaused by the high pressure steam pipes connecting an indirectresuperheater with the tubularheating surfaces of the steam generatorare eliminated.

"In certain cases, there is not enough room in the lines and in theparts of the steam generator where there is no radiant heat foraccommodating the whole resuperheater. In such cases, the partlyexpanded steam is conducted through the inner tubes and the highpressure fluid is conducted through the outer tubes, and at least apartof the heat transfer apparatus is placed, to receive heat by radiation,for example in the combustion chamber of the steam generator. In thiscase, the steam to be resuperheated is indirectly heated by the highpressure fluid, the latter receiving heat by radiation. The tubesconducting the partly expanded steam are shielded against radiant heatby the conduits conducting the high pressure fluid. This is importantbecause partly expanded steam does not always flow through the heattransfer apparatus, as is the case, for example, when the plant isstarted.

The heat transfer apparatus according to the invention may be used forregulating the resuperheat temperature. Control means may be connectedwith the tubular heating surfaces for the high pressure fluid, so thatthe high pressure fluid cools the partly expanded steam when the2,878,791 Patented Mar. 24, 1959 latter is too hot, and heats the partlyexpanded steam when the latter is too cool.

Though it may appear advantageous to arrange a plurality of inner tubesin each outer tube of the heat transfer apparatus, for improving .heattransfer, pressure, and constructional conditions, it will be preferablein most cases to arrange only one tube inside each outer tube,particularly if the tubes are bent to a hair pin configuration. Ifseveral hair pin units are connected in series, the heat transferapparatus may be in the form of a meander.

If the indirect heat transfer apparatus is placed outside of the steamgenerator, the individual heating tube of -the.latter must beconnectedby means of a header or collector, and a conduit must beprovided to connect .the header with a header connecting the individualelements of the indirect heat transfer apparatus. This is unnecessary,if the heat transfer apparatus is arranged inside the steam generatoraccording to the invention, so that pressure losses and cost arereduced. In certain cases, for example, if the temperature of the fluidon one side of the heat transfer apparatus must be controlled byinjecting water, the provision of a header may be advisabletointerconnect the tube sections conducting the fluid whose temperaturemust be controlled. The sectionsof the tubes conducting the other fluid,however, may be serially interconnected, avoiding headers. Colle'ctorsare also desirable, if the different tube sections are .not uniformlyheated. Since headers for this purpose are usually provided anyway inconnection with the tubular heating surfaces of a steam generator, thetubes of individual sections of the heat transfer apparatus arrangedaccording to the invention maybe connected in series.

'Though in this specification and in the claims the word steam is usedto specify the operating fluid of the power plant, the invention is notlimited topower plants using steam as operating fluid but is equallywell applicable to plants using other vapors as operating fluid.

"The novel features which are considered characteristic of the inventionare set forth with particularity in the appended claims. The inventionitself, however, and additional objects and advantages thereof will bestbe understood from the following description of embodiments thereof whenread in conjunction 'withthe accompanying drawing, in which Fig. 1 is adiagrammatic part sectional illustration of a power plant according tothe invention;

Fig. 2 is a diagrammatic part sectional illustration of 'a'portio'n of asteam generator forming'part of a power plant according to theinvention;

Fig. 3 is a part sectional diagrammatic illustration of a modificationof the p'art shown in Fig. 2;

Fig. 4 'is an illustration of a detail of a power plant according to theinvention;

Fig. 5 is a sectional'view of a detail of a power plant according to theinvention.

The same numerals designate the same parts in all figures.

Referring more particularly to Fig. 1 of the drawing, numeral '1designates a steam generator which is heated by a combustion apparatus2. Numeral 3 designates a combustion'chamb'er in which radiant heat andcombustion gases are produced. 'The combustion gases continue to passthrough a flue '4. An operating fluid, such as water, is supplied to thesteam generator through an inlet header 5. The water flows through tubes27 and :7 forming acombustion gash'eated feed water preheater,generallyknown as an economizer. The preheatedfeed water enters atubular heating surface 8 which :is used for lining the walls of thecombustion chamber 3 land is exposed to radiant heat. The steam formedin the heating surface section 8 is conducted through a conduit 9 into afirst superheater 10 and thereupon into a heat transfer apparatus 11which forms a second superheater and a resuperheater which will bedescribed later. The high pressure steam leaving the apparatus 11 passesthrough a third tubular superheating section 12 and therefrom through asteam main 13 into the high pressure part 14 of a prime mover, such as asteam turbine. The steam which is partly expanded in the prime mover 14is conducted through a conduit 15 into a tubular resuperheating surface16 and therefrom into tubes 21 which are arranged inside the tubesforming the second superheating surface for the high pressure steam. Theresuperheated steam is conducted through a conduit 17 into a lowpressure part 18 of the steam turbine plant. The high pressure turbine14 and the low pressure turbine 18 have a common shaft for driving anelectric generator 19. The steam exhausting from the low pressureturbine 18 is removed through a conduit 20. In the illustratedembodiment of the invention, the part of the steam generator, in whichheat is transferred by conduction and convection and not by radiation,is too small to accommodate the total required resuperheating surface.It is therefore necessary to arrange a part of the resuperheater in thecombustion chamber where it is exposed to radiant heat and where it ispreferably used for lining a wall portion of the combustion chamber.Since resuperheaters are not always cooled by fluid passingtherethrough, as is the case, for example, when starting the powerplant, the portions of the resuperheating surface which are exposed toradiant heat must be especially protected. This can be done by means ofcomplicated arrangements, including valves and the like, for passinghigh pressure fluid through the resuperheating tubes when no partlyexpanded steam is available. According to the invention, the protectionof the resuperheater against radiant heat is eflected in a much simplermanner. The partly expanded steam is conducted through tubes 21, whichare inside the tubes 22 of the heat transfer apparatus 11, the highpressure fluid being conducted through the annular space between thetubes 21 and 22. In the heat transfer apparatus 11, the resuperheatingsurface is heated by partly superheated high pressure steam, as is donein conventional indirectly heated resuperheaters which are arrangedoutside of the steam generator and which cause radiation losses. Suchlosses are avoided with the arrangement according to the presentinvention because the heating steam for the resuperheater gives off andreceives heat simultaneously and the temperature outside of the tubes 22is so high that no heat can radiate from the tubes 22 to the outside. Aheat transfer apparatus arranged according to the invention can be muchsmaller to do the same work as does a conventional steam heatedresuperheater. The heat transfer apparatus 11 includes a plurality oftubes arranged in parallel with respect to the flow of steamtherethrough. The plant according to the invention can be so arrangedthat the superheaters 10 and 12, the resuperheater 16, and the heattransfer apparatus 11 all have the same number of parallelly arrangedtubes. The number of headers can thereby be greatly reduced, becauseeach outer tube of the apparatus 11 can be connnected with a tube of thesuperheaters for the high pressure steam, and each inner tube 21 can beconnected with a tube of the resuperheater 16. Only the followingheaders are required: a header 23 at the inlet of the superheater 10, aheader 24 at the outlet of the superheater 12, a header 25 at the inletof the resuperheater 16, and a header 26 connected to the outlets of theinner tubes 21 of the heat transfer apparatus 11. The feed waterpreheater or economizer 27, 7 also includes a plurality of tubularelements arranged in parallel with respect to the flow of the fluidtherethrough.

The part of the economizer formed by the tubes 27 is 4 constructed as aheat transfer apparatus 6 including outer tubes 27 through which thefeed water is conducted, and inner tubes 28 arranged inside the tubes 27for conducting a heating fluid which is supplied from a header 29 andreturned into a header or collector 30. The heating fluid is preferablytaken from the circuit of the operating fluid of the power plant at apoint where the temperature of the operating fluid is higher than thatof the feed water entering the heat transfer apparatus 6. The heatingfluid may be steam bled from the turbine plant. The feed water passingthrough the outer tubes 27 is thus heated by the inner tubes 28. It maybe heated simultaneously by the combustion gases passing outside of thetubes 27. The combustion gases pre vent any case heat radiation andlosses to the outside.

Fig. 2 illustrates a modified arrangement according to the invention.The parts of the power plant not shown in Fig. 2 correspond to therespective parts shown in Fig. 1. Steam produced in the heating surfacesection 8 of the steam generator is conducted through a conduit 9 and aheader 23 into a first superheater 31 from which the superheated steamflows through a header 44, a conduit 32, and a header 45 into innertubes 33 of a heat transfer device 34. The high pressure steam leavingthe tubes 33 is collected in a header 46 and passes through a conduit 35and through an inlet header 24 into a second superheater 36. The highpressure steam superheated in the second superheater 36 is collected ina header 47 and conducted through a steam main 13 to a high pressureturbine. The partly expanded steam exhausting from the high pressureturbine is conducted through a conduit 15 and a header 25 into a firstcombustion gas heated resuperheater 37 and therefrom through outer tubes38 of the heat transfer apparatus 34. The partly expanded steam leavingthe tubes 38 is conducted through a second combustion gas heatedresuperheater 39 at whose outlet a header 26 is provided which isconnected, by means of a conduit 17, with the inlet of a low pressureturbine.

The heat transfer apparatus 34 constitutes a resuperheater which isheated by high pressure steam as well as by combustion gases. In thearrangement illustrated in Fig. 2, the combustion gases heat the partlyexpanded steam from the outside, whereas the high pressure steam flowingthrough the inner tubes 33 heats the partly expanded steam from theinside. The heat transfer apparatus can be used to serve not only as anormal resuperheater, but also as a temperature regulator for the steamto be resuperheated. The temperature of the high pressure steam can becontrolled by injecting water from a conduit 40 into the high pressuresteam conduit 32 which supplies heating steam to the heat transferdevice 34, and by injecting water through a conduit 41 into the highpressure steam conduit 35 through which heating steam is removed fromthe heat transfer apparatus 34. The amount of water injected through theconduit 40 into the conduit 32 is so controlled that the temperature ofthe steam in the inner tubes 33 is lower or higher than .the temperatureof the partly expanded steam flowing through the outer tubes 38 forcooling or heating, respectively, the partly expanded steam. The amountof water injected through conduit 41 into the conduit 35 is controlledto produce the desired steam temperature at the outlet of the highpressure superheater 36. A conduit 42 isprovided interconnecting theconduits 32 and 35, in which conduit a throttling means or valve 43 isarranged for controlling the flow of high pressure steam through theconduit 42. If the high pressure steam is cooled too much in the heattransfer device 34 and/or by injection of water from the conduit 40, hothigh pressure steam from conduit 32 can be by-passed through the conduit42 atound the device 34 and conducted into the superheater 3 Since thewater injection must affect all parallelly arranged tubes of the heattransfer device and of the high pressure steam superheater, headers 44,45, 46, and 47 must be provided in addition to the headers forming partof the system shown in Fig. 1. No headers are needed for interconnectingthe tubular elements forming the resuperheater heating surfaces 37 and39 with the outer tubes 38 of the heat transfer device 34.

Fig. 3 illustrates a modification of the heat transfer apparatus formingpart of the system according to Fig. 2. If the individual parallellyarranged tubular elements of the heat transfer apparatus 34 and/or ofthe resuperheaters 37 and 39 are not uniformly heated, the provision ofadditional headers 48, 48a, 49, and 49a may be advisable. The header 48amixes the steam coming from the tubes 37, and the header 48 distributesthe mixed steam into the outer tubes 38. The header 49 mixes the steamheated in the tubes 38, and the header 49a distributes the steam intothe tubes 39.

Fig. 4 illustrates an element 51 of a heat transfer apparatus. An innertube 53 is inserted in an outer tube 52, both tubes being bentsimultaneously to assume the con figuration of a hair pin. This methodof manufacture is particularly suitable for elements in which only oneinner tube is placed in the outer tube. A plurality of elements 51 maybe arranged in parallel with respect to fluid flow. If large heatingsurfaces are required, several elements 51 may be arranged in serieswith respect to fluid flow.

Fig. 5 illustrates a connection of an inner tube 53 with an outer tube52 and a direct connection, without header, of the outer tube 52 with atube 55 of a consecutive heating surface. One arm of an angular hollowmember 57 is pushed along the inner tube 53 until it abuts against theend face 56 of the outer tube 52 with which it is connected by a weld59. The end face of the other arm of the member 57 is welded to the endface of the tube 55 at 58. The member 57 has a sleeve portion which isconnected with the inner tube 53 by means of a weld 60.

The system according to the invention is particularly useful inconnection with a forced flow steam generator of the once-through type.It can be applied to steam or Vapor power plants operating at, above, orbelow the critical pressure of the operating fluid. The elements of theheat transfer apparatus may be arranged in the form of packages or maybe arranged in a plane, so that it can be used, for example, for liningor forming the combustion chamber wall or for forming baffles in largesteam generators.

What is claimed is: I

1. A steam generating, superheating, and resuperheating plant comprisinga combustion chamber, a flue connected with and receiving hot gases ofcombustion from said combustion chamber, heating tubes placed in saidcombustion chamber and in said flue for heating and evaporating waterflowing through said tubes, a superheater connected with said heatingtubes for receiving steam therefrom, said superheater including firsttubes placed within said flue for receiving heat substantially byconvection and second tubes connected in series relation with said firsttubes and being placed in said combustion chamber for receiving heatsubstantially by radiation, and a steam resuperheater having a firstportion placed within said flue for receiving heat from said hot gasesand having a second portion connected in series relation with anddownstream of said first portion with respect to the flow of the steamto be reheated, said second portion being placed inside of at least aportion of said second tubes of said superheater for exchanging heatwith the steam in said second tubes of said superheater.

2. A steam generating, superheating, and resuperheating plant as definedin claim 1, including an inlet header and an outlet headerinterconnecting a plurality of said second tubes of said superheater forconducting operating medium in parallel relation through said tubes,said second portion of said resuperheater including a plurality of tubesindividually disposed within the interconnected second tubes of saidsuperheater and having inlet and outlet portions extending through saidheaders.

3. A steam generating, superheating, and resuperheating plant accordingto claim 2 in which said inlet portions extend through said outletheader and said outlet portions extend through said inlet header.

References Cited in the file of this patent UNITED STATES PATENTS2,602,433 Kuppenheimer July 8, 1952 2,685,279 Caracristi Aug. 3, 19542,685,280 Blaskowski Aug. 3, 1954 FOREIGN PATENTS 275,236 Great BritainJuly 26, 1928 310,975 Great Britain June 12, 1930 383,569 Great BritainNov. 17, 1932 662,102 Great Britain Nov. 28, 1951

